Superfluidity and charged vortices in systems with spontaneous interlayer coherence in the low-density limit

The conditions for formation of a bound state between two-dimensional spatially separated electron and hole in a magnetic field normal to the plane of motion of the carriers are investigated. The binding energy, effective mass, and electric polarizability of the electron-hole pair are found as functions of the distance d between conducting layers. The features of the superfluidity of a Bose gas of electron-hole pairs in the case of low density are analyzed. It is established that quantized vortices in the superfluid phase have real electric charge, the value of which depends on the density of pairs and the distance between layers. In the case of small d and high magnetic fields the vortex charge q=νe, where ν is the filling factor of the lowest Landau level by carriers. The stability of the Bose gas of pairs against transition to the crystalline state is investigated, and it is shown that at small d the pair crystallization temperature T m is substantially below the superfluid transition temperature T c . With increasing d the temperature T m grows more rapidly than T c , and there exists a critical value d at which the superfluid phase vanishes.